[PATCH] D143136: [ELF] -z notext: avoid dynamic relocations in .eh_frame

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 494684.
MaskRay marked 3 inline comments as done.
MaskRay added a comment.

comments


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D143136/new/

https://reviews.llvm.org/D143136

Files:
  lld/ELF/Relocations.cpp
  lld/test/ELF/eh-frame-znotext.s


Index: lld/test/ELF/eh-frame-znotext.s
===================================================================
--- /dev/null
+++ lld/test/ELF/eh-frame-znotext.s
@@ -0,0 +1,30 @@
+# REQUIRES: aarch64
+## While a symbolic relocation for -z notext in .eh_frame can emit a dynamic
+## relocation, we try avoiding that (https://github.com/llvm/llvm-project/issues/60392)
+## and use a canonical PLT entry instead.
+
+# RUN: rm -rf %t && split-file %s %t && cd %t
+# RUN: llvm-mc -filetype=obj -triple=aarch64 a.s -o a.o
+# RUN: llvm-mc -filetype=obj -triple=aarch64 abi.s -o abi.o
+# RUN: ld.lld -shared abi.o -o abi.so
+
+# RUN: ld.lld a.o abi.so -o a
+# RUN: llvm-readelf -r --dyn-syms a | FileCheck %s
+# RUN: ld.lld -z notext a.o abi.so -o a
+# RUN: llvm-readelf -r --dyn-syms a | FileCheck %s
+
+# CHECK: R_AARCH64_JUMP_SLOT {{.*}} __gxx_personality_v0 + 0
+
+# CHECK: 1: 00000000002{{.*}} 0 FUNC    GLOBAL DEFAULT  UND __gxx_personality_v0
+
+#--- a.s
+foo:
+.cfi_startproc
+.cfi_personality 0, __gxx_personality_v0
+  ret
+.cfi_endproc
+
+#--- abi.s
+.globl __gxx_personality_v0
+.type __gxx_personality_v0, @function
+__gxx_personality_v0:
Index: lld/ELF/Relocations.cpp
===================================================================
--- lld/ELF/Relocations.cpp
+++ lld/ELF/Relocations.cpp
@@ -1079,7 +1079,15 @@
     return;
   }
 
-  bool canWrite = (sec->flags & SHF_WRITE) || !config->zText;
+  // Use a simple -z notext rule that treats all sections except .eh_frame as
+  // writable. GNU ld does not produce dynamic relocations in .eh_frame (and our
+  // SectionBase::getOffset would incorrectly adjust the offset).
+  //
+  // For MIPS, we don't implement GNU ld's DW_EH_PE_absptr to DW_EH_PE_pcrel
+  // conversion. We still emit a dynamic relocation.
+  bool canWrite = (sec->flags & SHF_WRITE) ||
+                  !(config->zText ||
+                    (isa<EhInputSection>(sec) && config->emachine != EM_MIPS));
   if (canWrite) {
     RelType rel = target->getDynRel(type);
     if (expr == R_GOT || (rel == target->symbolicRel && !sym.isPreemptible)) {


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